Measurements of resistance by the interrupter technique and of transcutaneous partial pressure of oxygen in young children during methacholine challenge

Abstract

Measurement of bronchial airway responsiveness requires noninvasive techniques in young children. The study was designed to examine the changes in resistance as measured using the interrupter technique (Rint) at the dose of methacholine (M) that induced a fall in transcutaneous partial pressure in O2 (P(tc)O2) > or = 20% (PD(20)P(tc)O2) in young children. Rint was calculated using the linear back-extrapolation method (Rint(L)) and the end-interrupter method (Rint(EI)). Twenty-two children (mean age, 5.2 +/- 1.1 years; range, 3.4 - 7.1 years) with nonspecific respiratory symptoms (mainly chronic cough, n = 17) were tested. P(tc)O2, Rint(L), and Rint(EI) were measured before the test, after saline challenge (baseline (B)), after each dose of M delivered by a dosimeter, and after bronchodilator (BD) inhalation. P(tc)O2 decreased significantly during M challenge, from 85 +/- 6 mmHg (B) to 62 +/- 9 mmHg (P < 0.05), and increased after BD inhalation, to 82 +/- 8 mmHg. Rint(L) and Rint(EI) increased significantly during M challenge, from 0.94 +/- 0.2 KPa/L/s and 1.11 +/- 0.19 KPa/L/s (B) to 1.27 +/- 0.35 KPa/L/s and 1.47 +/- 0.37 KPa/L/s, respectively (P < 0.05), and decreased after BD inhalation to 0.80 +/- 0.17 KPa/L/s and 0.95 +/- 0.18 KPa/L/s, respectively. Nineteen of 22 children reached the PD(20)P(tc)O2 at a dose of M ranging from 50-400 microg. At the PD(20)P(tc)O2, significant changes in Rint(L) and Rint(EI) (sensitivity index (SI) > or = 2) were found in 79% and 63% of children, respectively. We conclude that: 1) M challenge using P(tc)O2 is safe in young children; and 2) our findings are not in favor of the use of Rint as the only indicator of bronchial reaction in young children during M challenge.

The Tools of the Trade – Physiological Measurements of the Lungs

“…In addition, several studies show the usefulness of R int in evaluating airway response to methacholine in asthmatic preschool children, although its sensitivity is reported to be lower than that of sR aw [15,32,33].…”

Evaluación de la medición de las resistencias pulmonares por técnica de interrupción

“…Además, se exigió que la dispersión de las medidas fuera menor o igual al 20%. 22 En un grupo de pacientes se midió la Rint en dos ocasiones separadas en el tiempo para evaluar la reproducibilidad de la medida. Además, se realizaron medidas con boquilla, con pinza nasal y con sujeción de las mejillas, y sin ninguna de ellas, para valorar la posible influencia de esas variables.…”

Amplitude analysis of pressure oscillations after interruption of tidal breathing in preschool children

“…The interrupter resistance (R int ) measurement has been used to determine bronchodilator response (BDR) [1], [2] and also bronchial hyperresponsiveness (BHR) in young children [3]- [5]. Significance of the decrease or increase in R int values has to be assessed in those tests, respectively.…”